[Docs] Fix broken url and filename (swiftlang#33318)

Author: gabeiglio

docs/README.md

@@ -105,7 +105,7 @@ documentation, please create a thread on the Swift forums under the
   - [RequestEvaluator.md](/docs/RequestEvaluator.md):
     Describes the request evaluator architecture, which is used for
     lazy type-checking and efficient caching.
-  - [Literal.md](/docs/Literal.md):
+  - [Literals.md](/docs/Literals.md):
     Describes type-checking and inference specifically for literals.
 - [Serialization.rst](/docs/Serialization.rst):
   Gives an overview of the LLVM bitcode format used for swiftmodules.